Motorizing a B♭ clarinet 🤖

I am a quite amateurish clarinetist myself but I always liked to experiment with my instrument. Within this project I managed to add two robotic fingers which push two of the side-keys of the clarinet. Those keys are traditionally used for trills and for multiphonics, but their usage distracts the right hand of the performer from its common position. By robotizing the side-keys, they can be opened and closed while the right hand is free to operate on the lower half of the clarinet. After building the whole thing I wrote a piece for Natalie Eriksson.

You can also find the track on Spotify, part of my CD "The Expanded Body".

Apart from that, motorized keys can provide extreme precision in time (allowing for polyrhythmic play with the two human hands) and extreme speeds, impossible for a human being to achieve.

I used Reaper.fm as a DAW environment. To the music score to be read by the clarinetist I synced a MIDI file (containing note events that control the solenoids) as well as the live electronic processes (filters, reverb and delays).

The mount

Two small solenoids are providing the pushing force. Since they need to be pointed above the side-keys, I have designed a mount that I printed in 3D: first in PLA, and then, after discovering that the heat caused by the solenoids actually was so high that the PLA started warping, I decided to go for a 3D printer (actually, a sinterer) which used nylon powder.

The mount is secured around the central joint of the clarinet with a small screw. This model was designed to fit a cheap 50€ clarinet, but then with some manual adjustments it proved to work well on a Buffet R13 clarinet.

In order to make the impact of the solenoids on the keys more soft, I 3D-printed some PLA caps into which the solenoids were screwed, and a "Bb key limiter", a small piece I added to avoid a sort of kickback happening on one of the automatized keys.

Circuit

The circuit is really simple. Look at my former tutorial, "The sound compass", from which this project is derived. Here is the schematics:

Max patch

Copy the following text and select "New from clipboard" under the file menu in Max in order to make the patch appear.

<pre><code>
----------begin_max5_patcher----------
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p.bmN
-----------end_max5_patcher-----------
</code></pre>

You should see more or less something like this:

The a and b button on the left are used to select your serial port.

The middle section of the patch receives notes from any MIDI device or software (you can double-click the notein object to select the appropriate port). Then it sorts the notes selecting notes 60 and 72 (C4 and C5), and understanding if they are note-ons (velocity > 0) or note-offs (velocity 0). The MIDI messages are translated into four values: 1, 2, 11 and 22. See the next paragraph to understand how Arduino will handle these values.

This means that to control the solenoids we can set up a MIDI file with C4 and C5 note messages; or we could use a MIDI keyboard to send live messages. The corresponding solenoids will be pushing for the exact duration of the note events.

The buttons on the right side of the Max patch are manual controls to test the solenoids.

Detail of the Arduino code

const int sol1 = 4;
const int sol2 = 2;

These first two lines declare the variables used for the two solenoid pins.

void setup() {
Serial.begin(9600); // open a serial connection to your computer
pinMode(sol1, OUTPUT);
pinMode(sol2, OUTPUT);
digitalWrite(sol1, LOW);
digitalWrite(sol2, LOW);
}

In the setup section the serial port is initialized. Pins 4 and 2 are set as outputs. A LOW value is then written to the solenoid pins just to make sure that they start with no voltage.

void loop() {
if (Serial.available()) {
byte    command = Serial.read();
Serial.print("command");
Serial.print("\t");
Serial.println(command);

For each loop iteration, the serial port delivers a byte called command, which we can see printed in the serial monitor.

Then the byte is tested against the four values: 1, 11, 2 and 22.

if (command == 1) {
digitalWrite(sol1, LOW);
}
if (command == 11) {
digitalWrite(sol1, HIGH);
}
if (command == 2) {
digitalWrite(sol2, LOW);
}
if (command == 22) {
digitalWrite(sol2, HIGH);
}
}
}

When the byte is 1 or 2, solenoid 1 or 2 respectively are deactivated. Conversely, when 11 and 22 are received, the corresponding solenoids are powered.